Priming techniques to enhance use dependent plasticity have been examined in stroke rehabilitation research. Priming can upregulate ipsilesional cortex and/or down regulate contralesional cortex to improve effectiveness of subsequent therapy. Most priming techniques are costly and approved only for research. Here, we describe a priming technique that is cost-effective and has the potential to significantly change clinical practice. Bilateral motor priming (BMP) uses bilateral, symmetrical, rhythmic movement to ready the motor cortex for functional limb training. A rocker is used so that the less affected limb can drive the more affected one in symmetrical wrist flexion and extension. Active range of motion of the affected wrist is not necessary, and, thus, BMP can be used in severely impaired participants. Beneficial aspects of bilateral motor priming (compared to priming using rTMS and tDCS) include the fact that BMP is: 1) cost-effective; 2) available to a larger pool of individuals due to a paucity of safety concerns; (3) does not require a skilled operator; and (4) can be used the clinic. Previous studies comparing bilateral priming plus therapy found the priming and therapy combination to be more effective than therapy alone. However, previous BMP studies have not used dose matched designs. This project compares two groups of randomly assigned participants receiving task specific training (TST). Seventy-six participants will be randomized to receive either fifteen 2-hour sessions (30 hours) of BMP + TST or the same dose matched 30 hours of TST alone. Participants will attend sessions 3 times per week for 5 weeks with possible missed sessions scheduled at week 6. Outcome measures will be collected at pre-intervention, post-intervention, and follow-up (6 weeks post discharge). Aim 1 will determine the magnitude of change in upper limb impairment and function in chronic stroke survivors who have undergone 5 weeks of BMP+TST. The primary outcome measure is the Fugl-Meyer Test of Upper Extremity Function (FMUE). The secondary outcome is the Chedoke Arm and Hand Activity Index, an assessment of bimanual functional tasks. We expect both groups to improve on behavioral measures from pre-to post-intervention. However, the BMP+TST group is expected to have larger improvements than the TST alone group. We also expect these measures to persist at follow-up (6 weeks post cessation of treatment) in the BMP+TST group but not in TST alone. Aim 2 will determine the effects of bilateral priming on cortical mechanisms as measured by transcranial magnetic stimulation (TMS). We expect to find changes in TMS parameters that reflect a greater balance of hemispheric excitability in the BMP+TST group only. We further hypothesize that increases in hemispheric excitability will be associated with improvements in the FMUE. Currently, there is no clinically demonstrated long-term effective treatment for individuals with severe chronic upper limb hemiparesis. It is important to identify treatments for this underserved and under-investigated population.